Relationship of octanol/water partition coefficient and molecular weight to cellular permeability and partitioning in s49 lymphoma cells

Imaging Reactive Oxygen Radicals in Excised Mouse Lung Trapped by Reaction with Hydroxylamine Probes Using 1 GHz Rapid Scan Electron Paramagnetic Resonance

PURPOSE

Oxidative stress is proposed to be critical in acute lung disease, but methods to monitor radicals in lungs are lacking. Our goal is to develop low-frequency electron paramagnetic resonance (EPR) methods to monitor radicals that contribute to the disease.

PROCEDURES

Free radicals generated in a lipopolysaccharide-induced mouse model of acute respiratory distress syndrome reacted with cyclic hydroxylamines CPH (1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine hydrochloride) and DCP-AM-H (4-acetoxymethoxycarbonyl-1-hydroxy-2,2,5,5-tetramethylpyrrolidine-3-carboxylic acid), which were converted into the corresponding nitroxide radicals, CP• and DCP•. The EPR signals of the nitroxide radicals in excised lungs were imaged with a 1 GHz EPR spectrometer/imager that employs rapid scan technology.

RESULTS

The small numbers of nitroxides formed by reaction of the hydroxylamine with superoxide result in low signal-to-noise in the spectra and images. However, since the spectral properties of the nitroxides are known, we can use prior knowledge of the line shape and hyperfine splitting to fit the noisy data, yielding well-defined spectra and images. Two-dimensional spectral-spatial images are shown for lung samples containing (4.5 ± 0.5) ×1014 CP• and (9.9 ± 1.0) ×1014 DCP• nitroxide spins. These results suggest that a probe that accumulates in cells gives a stronger nitroxide signal than a probe that is more easily washed out of cells.

CONCLUSION

The nitroxide radicals in excised mouse lungs formed by reaction with hydroxylamine probes CPH and DCP-AM-H can be imaged at 1 GHz.

A Roadmap for Building Waterborne Virus Traps

Outbreaks of waterborne viruses pose a massive threat to human health, claiming the lives of hundreds of thousands of people every year. Adsorption-based filtration offers a promising facile and environmentally friendly approach to help provide safe drinking water to a world population of almost 8 billion people, particularly in communities that lack the infrastructure for large-scale facilities. The search for a material that can effectively trap viruses has been mainly driven by a top-down approach, in which old and new materials have been tested for this purpose. Despite substantial advances, finding a material that achieves this crucial goal and meets all associated challenges remains elusive. We suggest that the road forward should strongly rely on a complementary bottom-up approach based on our fundamental understanding of virus interactions at interfaces. We review the state-of-the-art physicochemical knowledge of the forces that drive the adsorption of viruses at solid-water interfaces. Compared to other nanometric colloids, viruses have heterogeneous surface chemistry and diverse morphologies. We advocate that advancing our understanding of virus interactions would require describing their physicochemical properties using novel descriptors that reflect their heterogeneity and diversity. Several other related topics are also addressed, including the effect of coadsorbates on virus adsorption, virus inactivation at interfaces, and experimental considerations to ensure well-grounded research results. We finally conclude with selected examples of materials that made notable advances in the field.

In vitro blood brain barrier models: An overview

Understanding the composition and function of the blood brain barrier (BBB) enables the development of novel, innovative techniques for administering central nervous system (CNS) medications and technologies for improving the existing models. Scientific and methodological interest in the pathology of the BBB resulted in the formation of numerous in vitro BBB models. Once successfully studied and modelled, it would be a valuable tool for elucidating the mechanism of action of the CNS disorders prior to their manifestation and the pathogenic factors. Understanding the rationale behind the selection of the models as well as their working may enable the development of state-of-the-art drugs for treating and managing neurological diseases. Hence, to have realistic simulation of the BBB and test its drug permeability the microfluidics-based BBB-on-Chip model has been developed. To summarise, we aim to evaluate the advanced, newly developed and frequently used in vitro BBB models, thereby providing a brief overview of the components essential for in vitro BBB formation, the methods of chip fabrication and cell culturing, its applications and the recent advances in this technological field. This will be critical for developing CNS treatments with improved BBB penetrability and pharmacokinetic properties.

Intracellular fluorescence competition assay for inhibitor engagement of histone deacetylase

An intracellular fluorescence competition assay was developed to assess the capability of inhibitor candidates to engage histone deacetylase (HDAC) inside living cells and thus diminish cell uptake and staining by the HDAC-targeted fluorescent probe APS. Fluorescence cell microscopy and flow cytometry showed that pre-incubation of living cells with candidate inhibitors led to diminished cell uptake of the fluorescent probe. The assay was effective because the fluorescent probe (APS) possessed the required performance properties, including bright fluorescence, ready membrane diffusion, selective intracellular HDAC affinity, and negligible acute cytotoxicity. The concept of an intracellular fluorescence competition assay is generalizable and has broad applicability since it obviates the requirement to use the isolated biomacromolecule target for screening of molecular candidates with target affinity.

Endosidin20-1 is more potent than endosidin20 in inhibiting plant cellulose biosynthesis and molecular docking analysis of cellulose biosynthesis inhibitors on modeled cellulose synthase structure

Endosidin20 (ES20) is a recently identified cellulose biosynthesis inhibitor (CBI) that targets the catalytic site of plant cellulose synthase (CESA). Here, we screened over 600 ES20 analogs and identified nine active analogs named ES20-1 to ES20-9. Among these, endosidin20-1 (ES20-1) had stronger inhibitory effects on plant growth and cellulose biosynthesis than ES20. At the biochemical level, we demonstrated that ES20-1, like ES20, directly interacts with CESA6. At the cellular level, this molecule, like ES20, induced the accumulation of cellulose synthase complexes at the Golgi apparatus and inhibited their secretion to the plasma membrane. Like ES20, ES20-1 likely targets the catalytic site of CESA. However, through molecular docking analysis using a modeled structure of full-length CESA6, we found that both ES20 and ES20-1 might have another target site at the transmembrane regions of CESA6. Besides ES20, other CBIs such as isoxaben, C17, and flupoxam are widely used tools to dissect the mechanism of cellulose biosynthesis and are also valuable resources for the development of herbicides. Here, based on mutant genetic analysis and molecular docking analysis, we have identified the potential target sites of these CBIs on a modeled CESA structure. Some bacteria also produce cellulose, and both ES20 and ES20-1 inhibited bacterial cellulose biosynthesis. Therefore, we conclude that ES20-1 is a more potent analog of ES20 that inhibits intrinsic cellulose biosynthesis in plants, and both ES20 and ES20-1 show an inhibitory effect on bacterial growth and cellulose synthesis, making them excellent tools for exploring the mechanisms of cellulose biosynthesis across kingdoms.

Benefits of Zebrafish Xenograft Models in Cancer Research

As a promising in vivo tool for cancer research, zebrafish have been widely applied in various tumor studies. The zebrafish xenograft model is a low-cost, high-throughput tool for cancer research that can be established quickly and requires only a small sample size, which makes it favorite among researchers. Zebrafish patient-derived xenograft (zPDX) models provide promising evidence for short-term clinical treatment. In this review, we discuss the characteristics and advantages of zebrafish, such as their transparent and translucent features, the use of vascular fluorescence imaging, the establishment of metastatic and intracranial orthotopic models, individual pharmacokinetics measurements, and tumor microenvironment. Furthermore, we introduce how these characteristics and advantages are applied other in tumor studies. Finally, we discuss the future direction of the use of zebrafish in tumor studies and provide new ideas for the application of it.

In-vitro blood-brain barrier models for drug screening and permeation studies: an overview

The blood-brain barrier (BBB) is comprised of brain microvascular endothelial central nervous system (CNS) cells, which communicate with other CNS cells (astrocytes, pericytes) and behave according to the state of the CNS, by responding against pathological environments and modulating disease progression. The BBB plays a crucial role in maintaining homeostasis in the CNS by maintaining restricted transport of toxic or harmful molecules, transport of nutrients, and removal of metabolites from the brain. Neurological disorders, such as NeuroHIV, cerebral stroke, brain tumors, and other neurodegenerative diseases increase the permeability of the BBB. While on the other hand, semipermeable nature of BBB restricts the movement of bigger molecules i.e. drugs or proteins (>500 kDa) across it, leading to minimal bioavailability of drugs in the CNS. This poses the most significant shortcoming in the development of therapeutics for CNS neurodegenerative disorders. Although the complexity of the BBB (dynamic and adaptable barrier) affects approaches of CNS drug delivery and promotes disease progression, understanding the composition and functions of BBB provides a platform for novel innovative approaches towards drug delivery to CNS. The methodical and scientific interests in the physiology and pathology of the BBB led to the development and the advancement of numerous in vitro models of the BBB. This review discusses the fundamentals of BBB structure, permeation mechanisms, an overview of all the different in-vitro BBB models with their advantages and disadvantages, and rationale of selecting penetration prediction methods towards the critical role in the development of the CNS therapeutics.

Model systems for studying the blood-brain barrier: Applications and challenges

The blood-brain barrier (BBB) poses a serious impediment to the delivery of effective therapies to the central nervous system (CNS). Over time, various model systems have been crafted and used to evaluate the complexities of the BBB, which includes an impermeable physical barrier and a series of energy-dependent efflux pumps. Models of the BBB have mainly sought to assess changes in endothelial cell permeability, the role of ATP-dependent efflux transporters in drug disposition, and alterations in communication between BBB cells and the microenvironment. In the context of disease, various animal models have been utilized to examine real time BBB drug permeability, CNS dynamic changes, and overall treatment response. In this review, we outline the use of these in vitro and in vivo blood-brain barrier model systems to study normal physiology and diseased states. These current models each have their own advantages and disadvantages for studying the response of biologic processes to physiological and pathological conditions. Additional models are needed to mimic more closely the dynamic quality of the BBB, with the goal focused on potential clinical applications.

Understanding brain penetrance of anticancer drugs

This paper explicates the impact of tumor capillary permeability for glioma World Health Organization (WHO) grades II to IV on brain-penetrant drug entry and distribution within the tumor and the brain adjacent to tumor (leading edge). In addition, we consider the distribution of non-brain penetrant drugs and how, in some cases, large-molecular-weight drugs might achieve good distribution into tumor and brain adjacent to tumor.

The effect of regadenoson on the integrity of the human blood-brain barrier, a pilot study

Regadenoson is an FDA approved adenosine receptor agonist which increases blood-brain barrier (BBB) permeability in rodents. Regadenoson is used clinically for pharmacologic cardiac stress testing using SPECT or CT imaging agents that do not cross an intact BBB. This study was conducted to determine if standard doses of regadenoson transiently disrupt the human BBB allowing higher concentrations of systemically administered imaging agents to enter the brain. Patients without known intracranial disease undergoing clinically indicated pharmacologic cardiac stress tests were eligible for this study. They received regadenoson (0.4 mg) followed by brain imaging with either ^99mTc-sestamibi for SPECT or visipaque for CT imaging. Pre- and post-regadenoson penetration of imaging agents into brain were quantified [SPECT: radioactive counts, CT: Hounsfield units (HU)] and compared using a matched-pairs t-test. Twelve patients (33% male, median 60 yo) were accrued: 7 SPECT and 5 CT. No significant differences were noted in pre- and post-regadenoson values using mean radionuclide counts (726 vs. 757) or HU (29 vs. 30). While animal studies have demonstrated that regadenoson transiently increases the permeability of the BBB to dextran and temozolomide, we were unable to document changes in the penetration of contrast agents in humans with intact BBB using the FDA approved doses of regadenoson for cardiac evaluation. Further studies are needed exploring alternate regadenoson dosing, schedules, and studies in patients with brain tumors; as transiently disrupting the BBB to improve drug entry into the brain is critical to improving the care of patients with CNS malignancies.

Applied Concepts in PBPK Modeling: How to Build a PBPK/PD Model

The aim of this tutorial is to introduce the fundamental concepts of physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) modeling with a special focus on their practical implementation in a typical PBPK model building workflow. To illustrate basic steps in PBPK model building, a PBPK model for ciprofloxacin will be constructed and coupled to a pharmacodynamic model to simulate the antibacterial activity of ciprofloxacin treatment.

Disulfide-Linked Dinitroxides for Monitoring Cellular Thiol Redox Status through Electron Paramagnetic Resonance Spectroscopy

Intracellular thiol-disulfide redox balance is crucial to cell health, and may be a key determinant of a cancer's response to chemotherapy and radiation therapy. The ability to assess intracellular thiol-disulfide balance may thus be useful not only in predicting responsiveness of cancers to therapy, but in assessing predisposition to disease. Assays of thiols in biology have relied on colorimetry or fluorimetry, both of which require UV-visible photons, which do not penetrate the body. Low-frequency electron paramagnetic resonance imaging (EPRI) is an emerging magnetic imaging technique that uses radio waves, which penetrate the body well. Therefore, in combination with tailored imaging agents, EPRI affords the opportunity to image physiology within the body. In this study, we have prepared water-soluble and membrane-permeant disulfide-linked dinitroxides, at natural isotopic abundance, and with D,(15)N-substitution. Thiols such as glutathione cleave the disulfides, with simple bimolecular kinetics, to yield the monomeric nitroxide species, with distinctive changes in the EPR spectrum. Using the D,(15)N-substituted disulfide-dinitroxide and EPR spectroscopy, we have obtained quantitative estimates of accessible intracellular thiol in cultured human lymphocytes. Our estimates are in good agreement with published measurements. This suggests that in vivo EPRI of thiol-disulfide balance is feasible. Finally, we discuss the constraints on the design of probe molecules that would be useful for in vivo EPRI of thiol redox status.

Leakiness and size exclusion of paracellular channels in cultured epithelial cell monolayers-interlaboratory comparison

PURPOSE

To determine and compare the paracellular characteristics of permeability (Papp) of Caco (-2), MDCK, and 2/4/A1 cell lines.

METHODS

The Papp data from 14 studies were analyzed by weighted nonlinear regression in terms of the paracellular parameters: porosity-pathlength (epsilon/delta), pore radius (R), and electrostatic potential drop (deltaphi). Aqueous diffusivities, Daq, for the analysis, were empirically determined. The required hydrodynamic radii, rHYD, were estimated without knowledge of compound density. Mannitol iso-paracellular profiles allowed comparisons of "leakiness" across labs.

RESULTS

Daq (37 degreeC) was predicted as 9.9x10(-5) MW(-0.453); rHYD=(0.92+21.8 MW(-1))xrSE, where rSE is the Stokes-Einstein radius. Values of pore radius ranged from 4.0(+/-0.1) to 18(+/-3) A, with the 2/4/A1 indicating the largest pores. The epsilon/delta capacity factor ranged from 0.2 (+/-0.1) to 69 (+/-5) cm(-1), with most values <1.5 cm(-1). The average potential drop for Caco-2 models was deltaphi(wt avg) Caco(-2)=(-43)+/-20 mV. The paracellular model predicted measured log Papp values with pooled r2=0.93 and s=0.17 (n=108).

CONCLUSION

R and epsilon/delta are negatively correlated to a large extent. Papp can be rate-limited by either factor, with a wide range of possible combinations still indicating nearly constant leakiness for a given marker.

Prediction of drug distribution into human milk from physicochemical characteristics

Decisions about the safety of breast feeding during maternal ingestion of drugs require knowledge of the amount of drug which might be present in the milk. For many drugs this has not been studied, and mothers are usually advised against breast feeding. In many cases this is undoubtedly unnecessary, as the total dose to which the baby is exposed is often negligible. It would be very helpful, therefore, to be able to predict the approximate amount of drug which might be present in milk. Existing theory of pH partitioning enables estimation of the distribution of unbound drug, i.e. milk: plasma unbound ratios. However, these ratios are poor estimates of the concentration ratios for whole milk, because whole milk contains proteins and lipid in which drugs will distribute in amounts which depend on their particular physicochemical properties. To predict the milk: plasma concentration ratios for whole milk the amount of drug present in the protein and lipid phases must be considered along with the unbound drug distribution. A 'phase distribution model' has therefore been developed which permits estimation of whole milk: plasma concentration ratios. The model requires a knowledge of the unbound drug concentration ratio, the plasma and milk unbound fractions and the milk lipid: ultrafiltrate partition coefficient. Evaluation of the model by comparison of predicted whole milk ratio values with literature milk: plasma area under the curve (AUC) ratios indicated a trend to overprediction for acidic and neutral drugs and underprediction for basic drugs. Transformation of the phase distribution equation by taking logarithms results in a relationship which can be analysed by multiple linear regression to derive predictive equations for acidic and basic drugs which take into account the relative contributions of each component of the model. Regression of the logarithms of the literature milk: plasma AUC values against the independent variables resulted in good correlations for acidic and basic drugs. The independent variables explained 93.1% and 82.9% of the variance in the values for acidic and basic drugs, respectively, with random scatter of residuals. The equations, together with those to predict unbound fractions of drug in milk and milk lipid: ultrafiltrate partition coefficients, enable the ratio of the milk: plasma AUCs to be estimated for any acidic or basic drug for which the distribution into human milk is not known, using the pKa, octanol: water partition coefficient and plasma protein binding values of the drug. The data set for neutral drugs (n = 3) was too small to develop a correlation equation.(ABSTRACT TRUNCATED AT 400 WORDS)